[hpsdr] Hermes transmit baseband frequency reversal ?

[Phil Harman]

Hi Tom, 

It’s not a bug, its a feature.  In order to get the correct sideband out of the CORDIC used in Penelope many years ago I needed to swap the I&Q inputs.  I guess PowerSDR had them reversed since day one and its been carried forward ever since. 

Not game to change at this late stage.....

73 Phil....VK6PH 

From: Tom McDermott 
Sent: Thursday, March 13, 2014 6:26 PM
To: hpsdr at lists.openhpsdr.org 
Subject: [hpsdr] Hermes transmit baseband frequency reversal ?

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HI,

In playing with some gnuradio sources, I am getting a baseband frequency reversal going through Hermes.
This using the definitions for I and Q in the HPSDR USB protocol document (ver 1.43).

That is - a downward frequency chirping IQ baseband signal into transmit causes an upward chirping
IQ baseband signal at the receive output.

It appears that the transmit I & Q side is doing the reversal, while the receiver seems to be normal, by testing this with an external SSB receiver, and by using various gnuradio instrumentation.


In looking through my own code that formats I & Q into the transmit frame, I cannot seem to find any
deviation from the protocol specification (rev 1.43).  Do I have a bug in my code, or is there a known 
issue with Hermes that causes the frequency sign inversion on transmit?

-- Tom, N5EG



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